1. Field
The aspects of the disclosed embodiment generally relate to substrate transports and, more particularly, to robotic substrate transports.
2. Brief Description of Related Developments
Generally substrate transport apparatus used in, for example, transporting semiconductor wafers or substrates have a transport arm and one or more end effectors for holding the substrates rotatably coupled to the transport arm at a common wrist joint. As such, the end effectors are allowed to rotate relative to one another about the common wrist axis. Where the substrate transport apparatus has more than one end effector, the end effectors are generally coaxially stacked at the common wrist joint where all electronic and/or vacuum connections as well as drive components pass through the transport arm and into each of the end effectors through the common wrist joint (where the electrical and pneumatic connections for the upper end effectors in the stack pass through the lower end effectors). However, it may become costly and difficult to route the electrical wires and pneumatic (including vacuum) lines to each end effector through the common wrist joint (and through the stack of end effectors) because of the relative motion that is required between each end effector in the stack of end effectors, the wrist pivot joint and the remaining transport arm components. For example, electrical wire/pneumatic line twist may occur limiting rotation of the end effectors and/or kinking of the pneumatic lines may occur. Slip rings and other rotational electrical/pneumatic couplings may be provided however this may increase manufacturing and operational (i.e. maintenance) costs associated with the substrate transport apparatus.
It would be advantageous to provide a substrate transport that allows for multiple independently rotatable end effectors that are disposed adjacent one another on a common axis of rotation and having substantially direct routing of wires and pneumatic lines to each end effector.